Various gases, e.g. methane or natural gas are stored and/or transported in the liquid state at a very low temperature, e.g. 160.degree. C., and to use them, it is necessary to bring them to a temperature close to ordinary temperature and to the gaseous state. Said revaporization takes place usually at a fairly high pressure, e.g. about 100 bars, in heat exchangers of the running water type which are constituted by nests of tubes through which the product to be revaporized passes and over whose surface water runs.
The tubes which form the nest are welded to an inlet manifold where the product is brought in under pressure at low temperature and in the liquid state and to an outlet manifold where the vaporized product is at about the same pressure as at the inlet but is at a temperature close to ambient temperature.
Up till now, aluminium alloy of the A-GS type containing magnesium and silicon or of the A-Z5G type containing about 5% of zinc and magnesium in a smaller concentration have been used for manufacturing revaporizer apparatus.
These alloys give rise to difficulties as far as concerns their mechanical characteristics and welding. Further, they have the disadvantage of poor resistance to corrosion in contact with water containing chlorides, e.g. briny water which is frequently found in the neighbourhood of ports where methane transporter ships are unloaded. Corrosion occurs especially at the points where the tubes are welded to the manifolds.
It is obvious that other alloys could be used, but then, they give rise to production and shaping difficulties so that they can be used only in the form of very simply designed tubes and poor exchange coefficients are obtained. This makes it necessary to provide apparatuses of larger dimensions which are more expensive. The problem that arises is therefore that of obtaining a satisfactory combination between the kind of metal, the welding method and the design of the apparatus and, in particular, of the tubes.